_Towctrans passed the guest's descriptor to the host towctrans.
Dinkumware's <wctype.h> (xwcc.h) defines towlower(wc) as
_Towctrans(wc, 1) and towupper(wc) as _Towctrans(wc, 2), the values
FreeBSD's wctrans.c also uses for "tolower" and "toupper". UCRT reads
1 as toupper and other nonzero values as tolower, so on Windows
towlower(L'A') returned L'A' and towupper(L'a') returned L'a', while
towlower(L'a') returned L'A'. The host wint_t is 16 bits there, which
also turned WEOF into 0xffff. glibc's wctrans_t is a pointer to a
table that towctrans reads, so on Linux descriptor 1 or 2 is
dereferenced as an address.
_Towctrans now takes the guest's 32-bit wint_t and size_t descriptor.
1 and 2 map 0..255 through the C locale tables behind _Getptolower and
_Getptoupper and return other values unchanged. Any other descriptor
sets errno to EINVAL and returns wc unchanged, as FreeBSD's
towctrans_l does.
Yunus Shaikh
Nahuel Genchi
boykopovar